The use of contrast agents in diagnostic medicine is rapidly growing. In X-ray diagnostics, for example, increased contrast of internal organs, such as the kidneys, the urinary tract, the digestive tract, the vascular system of the heart (angiography), and so forth, is obtained by administering a contrast agent which is substantially radiopaque. In conventional proton MRI diagnostics, increased contrast of internal organs and tissues may be obtained by administering compositions containing paramagnetic metal species which increase the relaxivity of surrounding protons.
Often it is desirable to image or treat a specific organ or tissue. Effective organ or tissue-specific diagnostic agents accumulate in the organ or tissue of interest. Copending patent application Ser. No. 07/948,540, filed Sep. 22, 1992, titled "Treated Apatite Particles for Medical Diagnostic Imaging," which is incorporated herein by reference, discloses the preparation and use of apatite particles for medical diagnostic imaging. This patent application also describes methods for preparing apatite particles which provide organ or tissue-specific contrast. By carefully controlling the particle size and route of administration, organ specific imaging of the liver, spleen, gastrointestinal tract, or blood pool is obtained.
A need continues to exist for new and structurally diverse compounds for use as imaging agents. There is a further need to develop highly stable compounds with good relaxivity characteristics that show improved specificity for particular organs and tissues.